This invention relates to variable capacity vane compressors which are adapted for use as refrigerant compressors of air conditioners for automotive vehicles, and more particularly to vane compressors of this kind in which the timing of commencement of compression is varied to thereby control the capacity of the compressor.
A variable capacity vane compressor has conventionally been proposed e.g. by Japanese Provisional Patent Publication (Kokai) No. 62-129593 assigned to the same assignee of the present application, which is adapted for compressing refrigerant of an air conditioner for automotive vehicles.
The above conventional compressor comprises: a cylinder formed of a cam ring and a pair of front and rear side blocks closing opposite ends of the cam ring, one of the front and rear side blocks having at least one first inlet port formed therein; a rotor rotatably received within the cylinder; a plurality of vanes radially slidably fitted in respective slits formed in the rotor; a housing accommodating the cylinder and defining a suction chamber and a discharge pressure chamber therein; wherein compression chambers are defined between the cylinder, the rotor and adjacent ones of the vanes and vary in volume with rotation of the rotor for effecting suction of a compression medium from the suction chamber into the compression chambers through the at least one first inlet port, and compression and discharge of the compression medium; at least one second inlet port formed in the one of the front and rear side blocks which has the at least one first inlet port formed therein, the at least one second inlet port being located adjacent a corresponding one of the at least one first inlet port, and communicating the suction chamber with at least one of the compression chambers which is on a suction stroke; a pressure chamber formed in the one of the front and rear side blocks having the at least one first inlet port formed therein, and communicating with a zone under lower pressure and a zone under higher pressure; a control element for controlling the opening angle of the at least one second inlet port, the control element having a pressure receiving portion slidably fitted in the pressure chamber and dividing the pressure chamber into a first pressure chamber communicating with the zone under lower pressure and a second pressure chamber communicating with both the zone under lower pressure and the zone under higher pressure; the control element being angularly displaceable in response to a difference in pressure between the first and second chambers for causing the control element to vary the opening angle of the at least one second inlet port, to thereby cause a change in the timing of commencement of the compression of the compression medium and hence vary the capacity of the compressor; a biasing member for biasing the control element in a direction of increasing the opening angle of the at least one second inlet port; a low-pressure communication passage communicating the second pressure chamber with the zone under lower pressure; a high-pressure communication passage communicating the second pressure chamber with the zone under higher pressure; and valve means for selectively opening and closing the low-pressure communication passage and the high-pressure communication passage, the valve means being disposed to close the low-pressure communication passage and simultaneously open the high-pressure communication passage or to open the high-pressure passage after closing the low-pressure passage, when pressure within the zone under lower pressure exceeds a predetermined value, and to open the low-pressure communication passage and simultaneously effect one of closing and reduction of the opening area of the high-pressure communication passage or to open the low-pressure passage after closing the high-pressure passage when the pressure within the zone under lower pressure is below the predetermined value.
However, according to the conventional vane compressor, the biasing member is formed by a coiled spring, for example, which has a coiled body thereof fitted around a hub projecting integrally from the one of the side blocks at one end face remote from the rotor, with one end thereof engaged with the control element and another end thereof with the hub, respectively. With such arrangement, the coiled body of the coiled spring can have loops thereof brought into contact with each other, or can be brought into contact with the outer peripheral surface of the hub since the ends of the coiled spring are loosely supported by the control element and the hub of the one side block, thus undesirably causing a frictional force acting upon the control element. This frictional force acting upon the control element possibly results in a hysteresis in the angular displacement of the control element, thereby making it difficult to accurately control the control element and hence the capacity of the compressor.
Furthermore, in the conventional vane compressor, as shown in FIG. 1, the control element A is received and positioned in place within an annular recess B1 formed in the side block B with reference to the outer peripheral surface thereof, i.e., in such a manner that a part Al of the outer peripheral surface is kept in contact with the inner peripheral surface of the annular recess Bl of the side block B by the urging force of the coiled spring C. With such arrangement, the distance between the diametrical center or axis of the control element A and a point where the outer peripheral surface of the control element A is in contact with the inner peripheral surface of the annular recess Bl is so long that a large amount of frictional torque is caused to act upon the control element A, which results in a hysteresis in the angular displacement of the control element A, thereby making it difficult to accurately control the control element A and hence the capacity of the compressor.